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Consciousness in the Single Neuron

 

 
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Are the contents of conscious perception tied to individual brain cells? Can we use single neurons to determine someone’s subjective experience? A recent studies published in PNAS suggests otherwise: there are no specialized neurons that carry information about what enters awareness and what not. If one holds the picture of a butterfly in front of […]

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Posted April 17, 2007 by Bernard J. Baars

 
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Are the contents of conscious perception tied to individual brain cells? Can we use single neurons to determine someone’s subjective experience? A recent studies published in PNAS suggests otherwise: there are no specialized neurons that carry information about what enters awareness and what not. If one holds the picture of a butterfly in front of one eye and the image of an apple before the other, the brain gets into a deep dilemma. It must integrate the contradictory pictures to a meaningful whole. This situation inevitably leads to a fascinating phenomenon called “binocular rivalry“. During rivalry, perception alternates between the picture shown to one eye and that shown to the other one. In other words, the butterfly will be seen during some moments and the apple during others. It is as if the brain is unable to decide which eye to trust, and therefore constantly wavers back and forth between them.

stimulus-dependent activity patterns that are decisive for what reaches conscious awareness and what does notThere are neurons in the visual cortex, which become strongly active for certain pictures (such as that of a butterfly), but not for others. If one measures the activity of such a cell by means of tiny electrodes, it is often possible to determine which stimulus gets perceived at any moment during binocular rivalry. Interestingly, however, some cells do not seem to be affected by the spontaneous perceptual changes during binocular rivalry. Instead, they truthfully indicate that the stimulus that activates them is constantly present, regardless whether it is perceived or not. This observation raises the question of whether there are individual brain cells that differ in their characteristics from other cells so that their activity stands in direct connection with what we consciously perceive. To answer this question, scientists at the Max Planck Institute at Tuebingen, Germany repeated the experiment using another trick. After all, while one sees a certain image with one eye, one can replace the image in the other eye, without affecting awareness. The question was, would this manipulation nonetheless affect neuronal activity? To the surprise of the researchers, any exchange of the pictures had large effects on the activity of the recorded neurons. In fact, many cells lost their special characteristic and showed no more activity fluctuations during perceptual alternations. Other cells, however, which had been unaffected by perception before, began to indicate the perceptual alternation of the stimuli.

Whether an individual brain cell participates in conscious experiencing or not therefore seems to be flexibly determined. Based on these results, it is conceivable that it is not only fixed interconnections between neurons, but also stimulus-dependent activity patterns that are decisive for what reaches conscious awareness and what does not.

Author Information

Alex Maier was a graduate student at the Max Planck Institute for Biological Cybernetics in Tübingen, Germany. He is now a researcher within the Unit on Cognitive Neurophysiology and Imaging at the National Institute of Mental Health in Bethesda, MD.

References

  1. Alexander Maier, Nikos K. Logothetis, and David A. Leopold Context-dependent perceptual modulation of single neurons in primate visual cortex, Proceedings of the National Academy of Sciences

ABSTRACT Some neurons in the visual cortex alter their spiking rate according to the perceptual interpretation of an observed stimulus, rather than its physical structure alone. Experiments in monkeys have suggested that, although the proportion of neurons showing this effect differs greatly between cortical areas, this proportion remains similar across different stimuli. These findings have raised the intriguing question of whether the same neurons always participate in the disambiguation of sensory patterns and whether such neurons might represent a special class of cortical cells that relay perceptual signals to higher cortical areas. Here we explore this question by measuring activity in the middle temporal cortex of monkeys and asking to what degree the percept-related responses of individual neurons depend upon the specific sensory input. In contrast to our expectations, we found that even small differences in the stimuli led to significant changes in the signaling of the perceptual state by single neurons. We conclude that nearly all feature-responsive neurons in this area, rather than a select subset, can contribute to the resolution of sensory conflict, and that the role of individual cells in signaling the perceptual outcome is tightly linked to the fine details of the stimuli involved.


Bernard J. Baars

 


4 Comments


  1.  

    1. “It is as if the brain is unable to decide which eye to trust, and therefore constantly wavers back and forth between them.”
    I believe that the brain (the physical) deals with the situation quite ordinarily receiving the two objects internally just as if they are two pieces of dough entered into the oven to be baked.Neither the brain nor the the physical objects are conscious. The mind deals with them with efficiency and accuracy and interprets them to the observing “Self” which is going to choose between them. This moment could be one of hesitation : the Self wants to concentrate on one thing. This concentration on one thing entails less concentration/or intentional/ unintentional observation of the other object. The whole operation depends on the interest/desire of the Self to see this and not to see that. The mind (the mental) my be perplexed due to the hesitation of the “fickle Self” oscillation or even worse is its undecided status, the neutral position that may cause a blur.

    2. “The Max Plank Institute at Tuebingen , Germany” experiments as described above shows no valuable results that can be considered proof of a hypothesis or its reversal. The abstract’s last paragraph reads: “We conclude … of the stimuli involved. “( Pls.refer to the very last four lines). I argue that this conclusion is not scientifically accurate. There are implicit propabilities more than scientific facts. Nothing actually is reached at, and (if any)is likely to mislead.

    The experiments conducted are good and in the right path towards the targetted subject (consciousness), and more experiments are still required if promising outcomes are to be attained. Good luck.




  2.  

    Some how we tend to relate consciousness to mind.The bacteria E.Coli turns it’s cell wall to hydrophobic[from hydrophilic]when exposed to 5% NaCl solution.Geneticists explain this as temparary adaptive response which precludes further investigation.This is a behaviour controlled by programmed logic of the DNA of E.Coli thus suggesting that DNA might act as the brain.The fact that DNA molecules replicate themselves should lead one to think that DNA molecules are conscious.Further DNA molecules can repair themselves that is they are memory molecules. Thus if brain has mind genes must also have a mind which may be termed as genopsych.The details of the development of the model of genopsych are posted on the web page dmrsekhar.sulekha.com .




  3.  

    The Origin of Consciousness

    D.M.R. Sekhar

    Abstract
    Intelligence is the function of brain. The structure of brain and it’s location in the living organism have been changing as life forms evolved. A single cell organism has only DNA that can qualify for the status of brain. DNA molecules not only remember their structure but also produce their replicates, the properties that no other matter molecules posses and hence they are live. Live molecules [ for that matter all life forms] are alive as they are conscious of their existence.

    Plant Intelligence

    Are plants intelligent? Probably yes as Anthony Trewavas showes(1) certain aspects of plant intelligence. He says “as a species we are clearly more intelligent than other animals, it is unlikely that intelligence as biological property originated only with homosapiens. There should therefore be aspects of intelligent behavior in lower organisms from which our superlative capabilities are but the latest evolutionary expression”. Behavior is equated with movement in animal terms and majority of multi cellular plants are sessile because of their decision several billion years ago to gather energy via photosynthesis and hence movement has never been critical for plant survival as light is freely available. Rejection of that decision to gather energy by photosynthesis by primordial animal eukaryotic cell, ensured that movement became critical to find food and mates. At the end of the review the questions if the word intelligence can be used to describe the behavior of plants. If so how plants accomplish (intelligent behavior) in the absence of a brain and he calls this phenomenon “Mindless Mastery”.

    The Survivors and Intelligence

    The idea and arguments that plants may be intelligent, reminds this author a paper news that describes(2) a mango tree that walks. The mango tree (in Gujarat State, India) reportedly as old as 1200 years ( big in size, rich with foliage) lowers one of its branches to the ground some distance away from the trunk and roots itself. The new trunk starts growing as the old one dries after some time. The locals call it “chalto ambo” (in Gujarati language) which means walking mango tree. The lowering of the branch and its development into a new trunk is repeated periodically. Attempts to grow this tree at other places by graft have not succeeded. Goats will die if they drink sea water. But feral goats in the barren island of Andaman-Nicobar are reported (3) drinking seawater during dry period (December-May) when no fresh water is available in whole of the island. The goats of Andaman and the chalto-ambo are the rarest of the rare examples of survival and the phenomenon behind must be a special case of adaptive response.

    Intelligence may be defined/described in several terms(1) . In the view of this author, intelligence of a living organism is sensing a change in the environment (or a problem) imagining several options based on logic and or past experience (memory) or simply by hit and try basis to overcome (or solve) the problem, selecting (deciding) one or few of the options sequentially or simultaneously and expression of the selected option or options as (response or) behavior. The elements of “past experience” (which may differ from organism to organism) and “hit and try” introduce randomness in the behavior or the response of the organism. The organisms that show a response or behavior that best answer the changed environment (the problem) survive.

    The Brain

    Are living organisms without brain mindless? Do brain and mind carry the same meaning? For those to whom body-mind relations are a matter of study4, brain is a part of the physical body and mind is an abstract term (which probably may be described as software that runs the brain). Often neo-cortex is considered the brain. If behavior is to be related to intelligence and neo-cortex, then we have a problem as amygdala is known5 to control the emotional behavior. Hence while neo-cortex is said to be the logical brain, amygdala is known as brain of emotions. Both amygdala and neo-cortex are located in the head. Does it mean that headless creatures are brainless? Enteric Nervous System (ENS) also known6,7 as gut’s brain, is considered a single entity containing neurons, neurotransmitters and proteins that send messages between neurons and support cells. ENS has complex circuitry that enables it to learn, remember and produce gut feelings, functioning in ways similar to that of peripheral nervous system. Tubular animals have the nervous system in their guts and as life evolved animals needed a more complex brain and so developed the central nervous system, preserving the gut’s nervous system also. Hence it may be noted that the functions of the brain are performed by different systems operating from different locations of the body as the evolution proceeded.

    Decision Making Capacity

    Are psychic processes such as learning, remembering, taking decisions, intelligent behavior dependent on the existence of nervous system (which may be loosely called brain, as of now)? In other words, are organisms without nervous system brainless? And hence can’t take intelligent decisions? Escherichia Coli a bacteria has hydrophilic outer surface8 in normal aqueous media. The surface of E.Coli turns hydrophobic in 5% solution of sodium chloride. E.Coli takes a decision to turn its surface from hydrophilic to hydrophobic, thereby perturbs9 the structure of water near it’s outer surface in order to escape the inhospitable environment created by 5% solution of sodium chloride. This may be described as a temporary adaptive response of E.Coli occurring through genetic means. That is E. coli shows intelligent response (behavior) if subjected to conditions that are unfavorable to it’s survival and the response must be a decision taken by genetic means, i.e. by DNA material as E.Coli has no brain or nervous system. Thus one may say that the DNA molecules have all the features of a brain and can prompt intelligent behavior. The structure and operating mechanism of “brain” and “genetic material” (i.e. DNA) are quite different but they can perform similar functions such as “remembering”, “taking decisions” etc. See for example, diodes that work on the basis of thermo ionic emission of electrons and semiconductors of N-P junction are quite different in their construction and operating mechanism but perform similar function the one way flow of electrons.

    The DNA and Genome

    According to Frued10 all living organisms have two primary instincts, viz. (a) self preservation and (b) procreation. Analogy is that DNA (and RNA) molecules11,12 do have (a) self repairing capacity and (b) can replicate themselves. If we ignore the play of terms, self-repairing capability of DNA molecules is nothing but “self preservation” and replication of DNA molecules is nothing but “procreation”. In the terminology of genetics, adaptive response is not conscious but controlled by “genetic means” or heredity or an outcome of natural selection. Without getting entrapped in the terminology, we can see that DNA material has both the primary instincts (self preservation and procreation), functions as “brain” in that it can take logical decisions and can remember (it’s own structure for example) that results into intelligent behavior expressed as adaptive response. After all we have already noted that the word “brain” has no absolute meaning as, it has been changing locations (during evolution as ENS, amygdala, neo-cortex) and the original “brain” unmistakably is DNA whereas ENS, amygdala and neo-cortex are it’s peripherals developed during evolution. Thus, the origin of intelligence is same as that of the origin of life, that is the origin of DNA. It is false to assume that the decision making capacity is the exclusive property of brain (the nervous system). Decisions can be taken by living organism from different levels, including the genetic level which is primary. Nervous system (ENS, amygdala and neo-cortex) may not have control over genetic material (DNA) but genetic material can control nervous system (brain).

    DNA molecules have adenine-thymine [AT] and guanine-cytosine [GC] nucleotide pairs fixed as sequences along the twisted double helix. G is bound [triple bond] more strongly to C than A to [double bond] T and hence we expect the presence more GC pairs which surprisingly is not the case. Surprise as the GC pair content in higher organism is in the range of 40% to 45% only 13 which goes against the general version of the second law of thermodynamics 14 . The genome of mammals and birds are reported 15,16 to have a GC content varying from 30% to 60%. Further the genome may be classified 17 into putative isochores [regions or fragments] with varying content of GC pairs. The isochors are non randomly 18,19,20 arranged i e the genome is structured from the point of view of isochors. With stable [GC rich fragments] and unstable [AT rich or GC poor fragments] states the genome resembles an information processing device. Gene complexes such as bithorax, BX-C and antennapedia, ANT-C are reported 21,22 to play a central role in programming the development of organism. Biological rhythms in an organism are due to 23 gene clocks which are automatically aligned with the external planetary rhythms. The alignment of bio-rhythms with planetary rhythms suggests that the gene clocks in fact sense the external environment.

    The Thesis

    [1]The properties of DNA molecules suggest that they not only preserve themselves by remembering their structure [hence can repair themselves] but also procreate ie replicate. [2]The presence of GC poor regions [against the general version of the second law of thermodynamics] in the genome and the fact that gene complexes programme the development organism indicate that DNA molecules/genome are self programmable and are competent to process information. [3] Genes [clocks] can sense external environment and reset genomic functioning for example bio-rhythms. The self programming property of DNA molecules/genome may be termed as genopsych or genpsy. Genpsy imparts consciousness to DNA molecules/genome.

    Closing Remarks

    Thus the origin of consciousness is the origin of life itself that is the first appearance of DNA/genome. The property of genpsy explains the native intelligence of microorganism, plants etc. Genpsy is the extensive [self ordering/self programming] property of DNA/genome as entropy [the measure of disorder] is the extensive property of matter. At macro level placebo effect is the self ordering property of the brain which we may call the mind. Thus genpsy is to genes is as the mind to brain. It is genpsy, the additional property that distinguishes DNA/genome/organism from other matter molecules.

    REFERENCES
    1. Anthony Trewavas, Aspects of Plant Intelligence, Annals of Botany 92:1-20, 2003.
    2. Sanjiv Desai, A mango tree that walks with time, The Times of India, Ahmadabad, 13.9.2000.
    3. Ahlawat, SPS, Rai, SB and Senani, S. Seawater Consumption of Feral Goat of Barren Island, Biotropica, 25(3), 1993.
    4. Joseph R. Dunn, Re-Introducing the Soul: The Medical Vs the Psychotherapeutic Model : An Interview with Elio Frattaroli, Psychology Online Journal, The American Institute of Psychology and Health, Vol. 11, No. 12, Dec. 2001.
    5. Daniel Goleman, Emotional Intelligence, Bantam Books , New York, 1996.
    6. Michael. D, Gershon, Alcmene Chalazonipis, Taube. P, Rothman, From Neural Crest to Bowel: Development of the Enteric Nervous System, Journal of Neuro Biology, Vol. 24, No. 2, 1993.
    7. Sandra Blakeslee, There is a ‘brain’ behind gut feelings, The Times of India, New Delhi, 5.1.1996.
    8. Gaudin , AM, Flotation of Micro Organisms, Froth Flotation, 50th anniversary volume, Ed. D. W. Fruestnuea, AIME, New York 1962.
    9. Ernest Grunwald, Thermodynamic Properties of Non Polar Solutes in Water and Structure of Hydrophobic Hydration Shells, J. Am. Chem. Soc., Vol. 108, No. 19, 1986.
    10. Ernest Jones, Life and work of Sigmund Freud, Vol. 2, Basic Books Inc. New York, 1960.
    11. George Wald, The origin of life, Molecules to living cells, W.H. Freeman and Company, San Francisco, 1980.
    12. Philip C Hanawalt, Protein Structure and Function: Assembly of Viruses and Ribosomes, ibid.
    13. Volkenshtein ,M.V, Biophysics ,MIR Publishers, Moscow, 1983.

    14. Yeremin , E.N, Fundamentals of Chemical Thermodynamics ,MIR Publishers,Moscow,1983

    15. Bernardi,G. Isochores and the evolutionary genomics of vertebrates, Gene,241:3-17,2000.

    16. Meunier,J.,Laurent Duret,L., Recombination Drives the Evolution of GC content in Human Genome, Mol. Biol. Evol. 21[6]:984-990, 2004.

    17. Bernardi,G., ETAL ,The mosaic genome of warm blooded vertebrates, Science,228:953-958,1985.

    18. Galtier,N., Piganeau,G.,Mouchiround,D. and Duret,L.,GC content Evolution in Mammalian Genomes: The Biased Gene conversion Hypothesis, Genetics. 159: 907-911., 2001.

    19. Cohen,N., Dagan,T., Lewstone and Graur,D., GC composition of the Human Genome: In search of Isochores, Mol. Biol. Evol. 25[5]:1260-1272., 2005.

    20. Arndt,P.F., Hwa,T.,Petrov,D.A., Substantial Regional Variation in Substitution Rates in the Human Genome :Importance of GC content, Gene Density and Telomere Specific Effects, J.Mol. Evol. 60: 748-763. 2005.

    21. Lewis, E.B., A gene complex controlling segmentation in Drosophila, Nature, Vol.276, 565-570. 1978.

    22. Lewis.E.B., Clusters of Master Control Genes Regulate the Development of Higher Organism,JAMA,Vol.267.No.11,1524-1531,1992.

    23. Okamura, H., Circadian and Seasonal Rhythms- integration of mammalian circadian clock signals: from molecule to behavior , Journal of Endocrinology,177,3-6,2006.





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